Variable capacitor



Dec. 10, 1968 L. J. HAVILAND 3,416,050

VARIABLE CAPACITOR Filed Oct. 9, 1-967 United States Patent C) 3,416,050 VARIABLE CAPACITOR Lyman J. Haviland, Port St. Lucie, Fla, assignor to Hammond Corporation, Chicago, Ill., a corporation of Delaware Filed Oct. 9, 1967, Ser. No. 673,558 Claims. (Cl. 317-255) ABSTRACT OF THE DISCLOSURE An organ swell control mechanism that is essentially a double variable capacitor which is adapted to be rotated to proportion the capacitative coupling between one circuit and two other circuits on the basis of :a relatively small degree of arcuate movement between its coupling limits, such that it can be mechanically connected to the swell shoe of an organ by very simple linkage which need not include motion multiplying means. The capacitor includes multiple stator and rotor or scanner elements which are evenly arcuately displaced and a solid dielectric so as to achieve close and fixed interplate spacing.

Field of the invention Swell control mechanisms for electrical musical instruments.

Description of the prior art One of the basic types of swell control mechanisms used for many years in electrical organs is set forth in Patent No. 2,646,468 issued to John M. Hanert for Ear Response Compensated Volume Control Apparatus. As set forth in that patent, the principal idea is to regulate the signal coupling between a pair of input circuits and an output circuit by means of a variable capacitor arrangement. The capacitor system shown in that patent is effective for the purpose of fading between two signal circuits and has been used for many years without fundamental change, but inspection will show that the structure is comparatively expensive to manufacture.

Summary of the invention The principal idea behind the present invention is to provide :a swell control variable capacitor system which has substantially the attributes of the system described in the before mentioned patent, but which is much less expensive to manufacture and which occupies much less space while still obtaining the advantages of variable capacitative coupling.

It is, therefore, :an object of the present invention to provide an organ type swell control variable capacitor system which is inexpensive and compact and which is adapted for direct mechanical connection to the organ swell pedal without motion multiplying means, and which is substantially noise free in operation.

Other advantages and features of the invention will become apparent from the following description of a preferred embodiment of the invention.

Brief description of the drawing In the drawings in which similar characters of reference refer to similar parts throughout the several views:

FIG. 1 is a perspective view of the swell control capacitor with a portion of the control lever broken away;

FIG. 2 is a sectional view which may be considered as taken in the direction of the arrows substantially along the line 2,-2 of FIG. 1;

FIG. 3 is a perspective exploded view showing the principal elements of the swell control device disassembled, but properly oriented relative to each other; and

FIG. 4 is a transverse sectional view which may be con- 3,416,050 Patented Dec. 10, 1968 ice Description of the preferred embodiment The capacitor mechanism includes two identical side plates 10 and 12 which provide the stator sections and a rotor or scanner 14 positioned between and spaced from the plates 10 and 12 by thin dielectric discs or wafers 16 and 18. Both the stator elements 10 and 12 and the scanner 14 are star shaped for a purpose which will appear presently.

Each of the side plates 10 and 12 is generally square and is made from a piece of flat insulating material which is copper clad on one side. For this purpose a suitable material is a paper base phenolic laminate about of an inch thick which has what is referred to in the trade as a one ounce copper cladding on one side. This is a standard article of commerce, and therefore needs no additional description. Although the size of these plates will necessarily vary somewhat depending upon the capacity required, it has been found that for the particular purpose envisioned, plates a little over 1 /2 inches square are appropriate.

Using common circuit board techniques, a serpentine line 20 is etched through the copper cladding so as to separate the copper surface of each of the plates into two separate areas which are insulated from each other. As is apparent from the drawing, the serpentine line is so arranged so as to provide twelve equi-angularly spaced radial lines which are alternately interconnected near the center and near the periphery so as to provide a paddlebladed six-pointed star 22 surrounded by the remaining copper surfaces, which for convenience will be referred to as a hollow star 23. Essentially, the star 22 and the hollow star 23 are the same electrically with respect to the rotor, excepting that one is rotated 30 relative to the other. Also, whereas the blades of the star 22 are interconnected at the center, the blades of the hollow star 2.3 are interconnected at the periphery of the plates 10 and Holes are formed near the corners of the plates for the purpose of securing the plates together and the star 22 is laid out in such fashion that two of the opposite blades are somewhat longer than the others and extend toward opposite corners sufficiently to encompass two of the holes just referred to. These two holes through blades of the star 22 are indicated by the numeral 24, the other holes having the numeral 26. The reason for extending two of the star blades to encompass the holes 24 is that it facilitates providing electrical connections to the star 22, whereas the other holes 26 facilitate providing electrical connections to the hollow star 23.

The two plates 10 and 12 are alike and so when they free each other the star 22 of one faces the hollow star 23 of the other.

A hole 28 is provided at the center of each plate for passage of the rotor axle, the two holes 28 being in alignment when the plates are face to face. The etching process is conducted so as to remove a small circular area 30 of the copper material around the holes 28 so that an axle passed through the holes 28 will be electrically insulated from the copper surfaces.

The rotor or scanner 14 is a six bladed regular star formed of soft copper sheet about .020 thick. This star is also paddle bladed with the blades having substantially the same size and shape as the fixed stars 22, excepting for the star 22 extensions to the holes 24. The scanner is fixed upon an axle 34 in any suitable manner and the axle fits the holes 28 previously mentioned. As shown, the shaft 34 is formed of two telescoping pieces which are pressed and soldered together. During the soldering operation a pigtail flexible lead 35 can also be connected to provide an electrical connection to the scanner. Prior to assembly the scanner element with the shaft '34 secured thereto is placed between fiat faces in a hardened steel fixture and coined so as to insure that the blades are flat and of the proper thickness and that the shaft 34 is true.

At each side, the blades 32 of the scanner are insulated from the copper surfaces of the side plates and 12 by the previously mentioned insulating wafers 16 and 18. Although other similar substances could be substituted, one suitable material which is readily available is a uniform thickness epoxy resin bonded woven glass fiber fabric about three thousandths of an ich thick. Other thicknesses could be used, depending upon the blade areas and the capacity desired. The diameter of these discs is slightly less than the diameter of the scanner, an eighth of an inch or so, to provide clearance for a stop pin to be mentioned presently.

Assembly is accomplished by putting one of the insulating wafers, the disc 16 for instance, on its end of the shaft 34 and inserting this end of the shaft through the hole 28 in the plate 10. Fastening elements 36, such as hollow rivets, are inserted through the holes 26 and 24 from the outside of the plate 10 and two of these elements at adjacent corners pass through clips 38 for forming the electrical connections, one to the star 22 of plate 10 and the hollow star 23 of plate 12, and the other to the star 22 of plate 12 and the hollow star 23 of plate 10. Conductive spacing washers 40 which are accurately held as to thickness are then press fitted over the rivets. The other insulating wafer 18 is then put in place over its end of the shaft 34 and the plate 12 placed thereon. The rivets are then headed to secure the plates 10 and 12 together. The spacing washers electrically interconnect the stars and the hollow stars of the plates 10 and 12 and provide connections to the terminals 38 by way of the rivets 36.

The thickness of the spacing elements 40 is equivalent to the thickness of the scanner 14 plus the thickness of the two insulating wafers 16 and 18, plus about .004" to insure clearance, so that although the shaft 34 can turn easily to rotate the scanner 14, the scanner cannot wobble and change capacity for any particular angular setting. Note that if any slight wobble motion does take place, this is largely compensated for by the symmetrical construction from front to back, and also around the axis of rotation.

In one position of the scanner 14, all of its blades overlie and align with the blades of the star 22 of plate 10 and the hollow star 23 of plate 12, whereas rotation of 30 will bring all of the blades of the scanner 14 in alignment with blades of the hollow star 23 of plate 10 and the star 22 of plate 12. To limit the travel between these two extreme positions, it is convenient to drill a hole 44 through the two plates in alignment, the hole passing through one of the etched lines in a position just inside the periphery of the circle defined by the ends of the scanner plates 32 and outside the periphery of the insulating discs 16 and 18. An insulating pin 42 formed of nylon or similar material passes through this hole and is cemented in place. It is positioned through one of the slots between the scanner blades and thus limits the travel of the scanner to 30 if as is suggested, the pin has a diameter approximately equal to the etched line 20 width.

When the device is assembled as indicated, it will be seen that in one limit position of the scanner where the blades 32 are opposite the blades 22 of plate 10, maximum capacity is established from the scanner 14 to the star 22 of plate 10 and the hollow star 23 of plate 12. Under these conditions there will be extremely little capacity existing from the scanner 14 to the star 22 of plate 12 and the hollow star 23 of plate 10. When the scanner is turned to its other extreme position, the plates 32 will be lined up with the blades 22 of plate 12 and very little capacity will exist from the scanner 14 to the star 22 of plate 10 and the hollow star 23 of plate 12, whereas maximum capacity will be established from the scanner 14 to the star 22 of plate 12 and the hollow star 23 of plate 10.

The scanner shaft 34 is connected to an actuating lever 48 by means of a slip clutch indicated generally by the numeral 46 which may be of any suitable construction. As shown, the clutch is made up of a collar 50, secured to the shaft by a set screw 52 and providing a face against which the lever 48 is pressed by a spring washer 54. This clutch is so arranged that as the lever 48 is moved, the scanner 14 will turn therewith until one of the star edges engages the pin 42. Thereafter, the lever 48 will overtravel without straining any of the capacitor elements. Similarly, when the lever 48 is moved in the opposite direction, the scanner 14 will turn therewith until the opposite edge of the adjacent blade strikes the pin 42 and thereafter the lever 48 will overtravel.

The lever 48 is connected to the organ swell pedal by any suitable intervening linkage mechanism, such as that shown in the previously referred to patent for instance, so that when the shoe is pressed downwardly, the lever 48 is moved in one direction, whereas, when the shoe is returned the lever 48 will move in the opposite direction.

Since this potentiometer type variable capacitor system may be substituted for the variable capacitor shown in the previously mentioned patent, the same or generally simi* lar electrical circuits may be used. Those not familiar with such circuits are referred to that patent for a discussion of their structure and theory of operation. The two terminals 38 provide connections to the two stators and the pigtail 35 the connection to the scanner. This supplies all of the terminals required for substitution in the circuit shown in the previously granted patent which essentially provides for varying the coupling as between an input circuit and an amplifier and also includes an arrangement for coupling the amplifier input progressively to a third circuit as the main input circuit is decoupled. This third circuit changes the frequency response of the system to accommodate for varying frequency response characteristics of the ear at various loudness levels.

Although I have described my invention on the basis of a preferred embodiment, it will be appreciated that variations in the structure may be made without departing from the spirit and scope of the invention and that, there fore, the limits of the invention are to be determined by analysis of the accompanying claims. For example, all stars can have four or eight blades, and the angular motion of the rotor will be correspondingly increased or decreased, Also, the shapes of the blades of either the stars or the hollow stars can be varied if it is desired to provide different capacitance values in the two extreme positions for the outside circuits.

Having described my invention, what I claim is new, useful and desired to secure by Letters Patent of the United States is:

1. A capacitor mechanism comprising a pair of fixed fiat plates of insulating material, a fiat rotatable scanner plate disposed between said fixed insulating plates, said fixed plates on the faces adjacent said rotatable plate being clad with conductive material, a wafer of insulating material disposed between each of said conductive faces and said rotatable plate, each of said conductive faces being divided into a pair of separate conductive elements insulated from each other, one of said conductive elements being formed as a star with the blades of the star interconnected adjacent the center, the other of said conductive elements being formed to provide a hollow star with the blades interconnected at the periphery, the blades of said star being alternated with the blades of said hollow star with an insulating space providing a serpentine band therebetween, said rotatable plate being formed as a star similar to the fixed stars, a shaft extending through said insulating plates at the center of said fixed stars and connected to said rotatable plate, said fixed stars having clearance around said shaft to insulate said fixed stars from said shaft, means connecting said insulating plates together including means providing a space therebetween to accommodate the thickness of said rotatable plate and said wafers, means providing electrical connections to the stars and hollow stars in opposed sets, means providing an electrical connection to said rotatable plate, and means for oscillating said shaft.

2. A capacitor mechanism as called for in claim 1 in which the means for oscillating said shaft includes a slip clutch device permitting overtravel of the last said means relative to said shaft.

3. A capacitor mechanism as called for in claim 1 in which the fixed stars, the hollow stars and the rotatable plate all have a like plurality of blades.

4. A capacitor mechanism as called for in claim 1 including a stop member disposed outside the periphery of said wafers and inside the periphery of said rotatable plate to limit arcuate movement-of said plate to the included angle between the blades of said plate.

5. A capacitor mechanism comprising a pair of flat plates of insulating material, a flat rotatable plate disposed between said insulating plates, said insulating plates on the faces adjacent said rotatable plate being clad with conductive material, a wafer of insulating material disposed vbetween each of said conductive faces and said rotatable plate, each of said conductive faces being divided into a pair of separate conductive elements insulated from each other, one of said conductive elements being formed as a paddle bladed star with the blades of the star regularly arcuately distributed and interconnected adjacent the center, the other of said conductive elements being formed to provide a hollow paddle bladed star with the blades interconnected at the periphery, the blades of said star being alternated with the blades of said hollow star with a narrow insulating space providing a serpentine band therebetween, said rotatable plate being formed substantially to the shape of saidpaddle bladed stars, a shaft extending through said insulating plates at the center of said stars and connected to said rotatable plate, said stars having clearance around said shaft to insulate said stars from said shaft, means connecting said insulating plates together with the stars on one plate opposing the hollow stars on the other plate including means providing a space therebetween to accommodate the thickness of said rotatable plate and said wafers, means providing electrical connections to said stars and hollow stars in opposed sets, means providing an electrical connection to said rotatable plate, and means for oscillating said shaft.

References Cited UNITED STATES PATENTS 2,413,391 12/1946 Usselman 317-249 X LEWIS H. MYERS, Primary Examiner. ELLIOT GOLDBERG, Assistant Examiner.

US. Cl. X.R. 3 l7249; 334-82 

